The present invention relates generally to a cotton conveying system for a cotton harvester, and more specifically to a blockage detector for such a system.
Typical of cotton harvesters, harvesting units are supported forwardly of a main frame. Each harvesting unit includes a plant passage for receiving a row of cotton and a pair of upright picker drums supported adjacent the plant passage. Spindles on the drums extend into the passage and remove cotton from the plants, and upright doffer assemblies doff the cotton from the spindles and direct it through discharge openings into upright discharge structure or suction doors. The cotton is then removed from the discharge structure or suction doors by cotton conveying ducts which carry air jet nozzles to propel the cotton into a basket on the harvester. Frequently, debris in the area of the discharge openings, or a blockage in the discharge structure or conveying ducts, will cause a build-up of cotton near the doffer assemblies. If undetected, this build-up of cotton can cause serious damage to the harvesting unit. Fires can occur in the doffer area because of the friction between the build-up of cotton and the doffer assemblies.
Heretofore systems for detecting blockage have not been entirely satisfactory. Some systems utilizing differential air pressure resulting from cotton build-up or debris in the duct or discharge structure are very sensitive and expensive to build, and have not solved the problem of detecting a partial blockage near the doffer assemblies. Others use a sensitive thermistor bridge which senses an interruption in air flow. Bridge-type sensors must be carefully adjusted prior to the harvesting operation. Photocell systems have also been utilized to detect absence of cotton in a duct, but they often give false indications at the end of a row and are easily disabled by sap or dust blocking the light path.